1. Field of the Invention
The present invention relates to a liquid crystal display device which has a picture character display area for displaying picture characters, each of which is represented by a fixed pattern.
2. Description of the Related Art
In portable electronic devices such as electronic notebooks, portable telephones and the like, display of picture characters, each represented by a fixed pattern, is becoming indispensable for informing the outside of a variety of device conditions such as power consumption of battery, occurrence of fault, and the like. Particularly, liquid crystal devices coming on the market in recent years have both a moving image display area which is actively driven and a picture character display area which is statically driven in order to reduce the cost and space.
Known liquid crystal display devices are generally classified into a reflection type which utilizes reflection of external light, incident from the outside, to display an image, a transmission type which transmits light emitted from a light source such as a back light to display an image, and a reflection/transmission combined type which transmits a portion of light from a light source and reflects a portion of external light.
Japanese Patent Laid-Open No. 350151/2001, for example, discloses a conventional reflection type liquid crystal display device which has a picture character display area. This liquid crystal display device comprises a light reflecting layer and a color filter layer laminated on a transparent substrate in order; a common electrode made of ITO (Indium Tin Oxide) disposed on the color filter layer for displaying picture characters; a data electrode disposed opposite to the common electrode across a liquid crystal layer for displaying picture characters, and a dummy pattern disposed around the data electrode.
On the other hand, Japanese Patent Laid-Open No. 202282/1999, for example, discloses a conventional transmission type liquid crystal display device which has a picture character display area. In this liquid crystal display device, a light shielding film formed on a transparent substrate is formed with openings each shaped in a desired picture character which is displayed by transmitting light from a backlight through the opening.
Further, Japanese Patent Laid-Open No. 330827/2000, for example, discloses a conventional reflection type liquid crystal display device which has a moving image display area. This liquid crystal display device comprises a thin-film transistor formed on a transparent substrate in an inverse stagger structure; an insulating film deposited to overlay the thin-film transistor; and a reflective electrode formed on the insulating film, where the thin-film transistor has a drain electrode connected to the reflective electrode through an opening formed through the insulating film.
In addition, Japanese Patent No. 2955277, for example, discloses a conventional reflection/transmission combined type liquid crystal display device which has a moving image display area. This liquid crystal display device comprises a thin-film transistor formed on a transparent substrate in an inverse stagger structure; an insulating film deposited to overlay the thin-film transistor; a transparent electrode formed on the insulating film; a transparent conductive film connected to a drain electrode of the thin-film transistor through an opening formed through the insulating film; and a reflective area formed of a metal film on the transparent conductive film over the thin-film transistor and opening area.
In the conventional liquid crystal display device having a picture character display area, a picture character pixel electrode in the shape of a picture character comprised of a fixed pattern is formed in the same layer as a signal electrode for supplying a signal to the picture character pixel electrode, as in the liquid crystal display device described in the aforementioned Japanese Patent Laid-Open No. 350151/2001. Such a configuration implies a problem of a degraded display quality because wires are readily visible.
To solve this problem, it is contemplated that the picture character pixel electrode is formed in a layer different from a layer in which the signal electrode is formed. In this structure, when a contact is formed in an imperceptible size for connecting the picture character pixel electrode to the signal electrode, the inductance and resistance increase at the contact, possibly increasing distortions in signal waveform and a voltage drop. Since the liquid crystal display device is basically driven with an alternating current, the liquid crystal display device cannot display images in response even at a relatively low signal frequency as distortions in signal waveform and voltage drop are increased due to increased inductance and resistance, giving rise to a problem of a degraded display quality.